Weight Management Glossary: BMI, A1C, GLP-1 and Other Terms Explained

Anyone who starts looking into weight management runs into a wall of abbreviations: BMI, A1C, GLP-1, DEXA, and more. Knowing what they mean makes it easier to follow a conversation with a provider and to judge what you read online. This glossary groups the most common terms into four sections and explains each in plain language. It is educational and does not replace medical advice.

Body measurements

BMI (body mass index). A number calculated from height and weight. Under 18.5 is classed as underweight, 18.5 to 24.9 as healthy weight, 25 to 29.9 as overweight, and 30 or above as obesity. BMI is a screening tool. It does not distinguish muscle from fat or show where fat is carried, so providers use it alongside other information.

Waist circumference. A tape measurement around the abdomen. Fat carried around the middle is linked with higher health risk, and risk is generally considered elevated above 40 inches for men and 35 inches for women.

Body composition. The proportion of your weight that is fat, muscle, bone, and water. Two people with the same BMI can have very different body composition.

DEXA scan. An imaging test that uses low-dose X-rays to measure bone density and body composition.

Bioimpedance. A method used by many smart scales and handheld devices to estimate body composition with a small electrical current. Results vary with hydration and are best used to follow trends over time.

Lab values

Fasting glucose. Blood sugar measured after at least eight hours without food. Below 100 mg/dL is considered normal, 100 to 125 indicates prediabetes, and 126 or higher on two tests indicates diabetes.

A1C (hemoglobin A1C). A blood test reflecting average blood sugar over roughly three months. Below 5.7 percent is considered normal, 5.7 to 6.4 indicates prediabetes, and 6.5 or higher indicates diabetes.

Insulin resistance. A state in which the body's cells respond less well to insulin, so the pancreas produces more to keep blood sugar steady. It often comes before type 2 diabetes.

Lipid panel. A blood test that measures cholesterol and triglycerides, used to assess heart and blood vessel risk.

Thyroid tests. Blood tests, usually starting with TSH, that check how the thyroid gland is working. Thyroid problems can affect weight and energy.

Metabolism and diet terms

Calorie. A unit of energy. Food supplies calories, and the body uses them for everything from breathing to exercise.

Basal metabolic rate. The energy your body uses at complete rest to keep basic functions going. It accounts for most of the calories you use in a day.

Calorie deficit. Using more energy than you take in over a period of time.

Metabolic adaptation. The body's tendency to use less energy and increase hunger signals as weight goes down. It is a normal response, and it is one reason progress often slows.

Plateau. A period of several weeks with no meaningful change despite a consistent routine.

Maintenance. The phase focused on holding steady. It usually requires ongoing habits and follow-up.

Continuous glucose monitor (CGM). A small wearable sensor that tracks glucose levels through the day. CGMs were developed for people with diabetes, and some are now sold over the counter.

Medication and regulatory terms

GLP-1. A hormone released by the gut after eating. It signals fullness, slows stomach emptying, and plays a part in blood sugar control.

GLP-1 receptor agonist. A class of prescription medications that mimic the GLP-1 hormone. Semaglutide belongs to this class.

GIP. A second gut hormone involved in how the body handles nutrients. Tirzepatide acts on both GIP and GLP-1 receptors.

Titration. Starting a medication at a low dose and increasing it gradually under a provider's direction.

FDA-approved. A drug the FDA has reviewed and found to be safe and effective for a specific use, with manufacturing held to FDA standards.

FDA-cleared. A term used for many medical devices, meaning the FDA found the device substantially equivalent to one already on the market. It is not the same as approval of a drug.

Compounded medication. A medication prepared by a state-licensed pharmacy for an individual prescription. Compounded medications are not FDA-approved and are not reviewed by the FDA for safety, effectiveness, or quality. They are not generics.

Generic. An FDA-approved copy of a brand-name drug that has been shown to work the same way.

Dietary supplement. A product such as a vitamin, herb, or powder sold without a prescription. Supplements are not approved by the FDA and are not evaluated for effectiveness before sale.

Telehealth. Medical care delivered remotely by a licensed provider, by video, phone, or secure online forms.

How to use these terms

Numbers are most useful together and over time. A single reading rarely tells the whole story, and the right targets depend on your age, history, and goals. Bring your recent results and your questions to a provider, who can explain what your numbers mean for you.

Talking with a licensed provider

Nu Image offers online evaluations with licensed providers for weight management. A provider reviews your health history and measurements, explains the options available through Nu Image, and decides whether any prescription is appropriate for you.

This content is for educational purposes only and is not medical advice, diagnosis, or treatment. Compounded medications are prepared by state-licensed compounding pharmacies and are not reviewed or approved by the FDA for safety, efficacy, or quality. Prescription products require an online consultation with a licensed healthcare provider, who will determine whether a prescription is appropriate.